We propose a 2-site R34 to develop a brief, flexible, manualized intervention with supporting phone app to reduce the risk of suicidal behavior in adolescents with high suicidal ideation or a recent suicide attempt, during the transition from inpatient to outpatient care. This transition period is the highest risk period for attempted and completed suicide. Suicide is the 3rd leading cause of adolescent mortality, and there are currently no established interventions for suicidal teens. By developing a treatment that can be delivered on an inpatient unit prior to the transition to outpatient treatment, we anticipate being able to lower suicidal risk and increase the likelihood that participants will attend subsequent outpatient treatment. In keeping with the priorities of NIMH, this intervention aimed at reducing the risk of suicide and suicidal behavior will be trans-diagnostic. We term the intervention ASAP, with anticipated components: (1) Adherence- promoting engagement and adherence to treatment through motivational interviewing; (2) Safety planning; and (3) Affect Protection- selecting from a menu of techniques for maintaining positive affect (e.g. savoring and switching strategies, mobilizing social support, maintaining sobriety, and improving sleep). Each of these components will be delivered within a Motivational Interviewing framework for enhancing intrinsic motivation for change. Treatment is brief (6-8 hours), and flexibly delivered on inpatien units or in home visits prior to initiation of outpatient treatment. ASAP augments protective factors against recurrent suicidal behavior and includes the family in the treatment. A safety plan phone app to extend the impact of treatment will also be developed. Innovative features include: (1) delivery of an intervention at a time and place when suicidal risk is highest; (2) augmentation of protective factors against recurrent suicidal behavior, specifically by promoting development of positive affect, healthy sleep and social support; (3) a Safety plan phone app to extend the impact of treatment; and (4) liaison with the outpatient therapist to ensure continuity of care. Th specific aims are 5 treatment development phases: (1) Open semi-structured interviews with 5 suicidal teens and parents and 5 clinicians at each site on the proposed content and context of the proposed treatment; (2) Develop the ASAP modules, adherence/competence measures, and phone app, and repeat open interviews; (3) Open trial of ASAP in 10 adolescents (5 at each site); (4) Debrief patients and families, inpatient and outpatient providers, examine the impact of treatment on proximal indicators of suicidal risk, and revise accordingly; (5) Conduct an RCT of ASAP followed by Aftercare (AC) vs. AC alone in 80 suicidal teens (across both sites) to determine ASAP's feasibility, acceptability, impact on proximal targets (e.g., adherence to outpatient care, sleep, positive affect, substance use), suicidal ideation and behavior. ASAP, developed with and intended for community clinicians, has the potential to be a sustainable intervention to reduce the burden of adolescent suicidality.